Micromechanical component

ABSTRACT

The invention creates a micromechanical component, in particular an acceleration sensor, having a flexible spring device (F 1 , F 2 , F 3 ) for the spring mounting of a mass ( 3 ) over a substrate ( 4 ), the flexible spring device (F 1 , F 2 , F 3 ) being on the one hand connected with the mass ( 3 ) and being on the other hand anchored in the substrate ( 4 ). The flexible spring device (F 1 , F 2 , F 3 ) has at least one flexible spring element (F 2 , F 3 ) whose movability in relation to the substrate ( 4 ) is capable of being modified in order to modify the effective spring constant of the flexible spring device (F 1 , F 2 , F 3 )

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a micromechanical component, inparticular an acceleration sensor, having a flexible spring device forthe spring mounting of a mass over a substrate, the flexible springdevice being connected on the one hand with the mass and on the otherhand being anchored in the substrate.

[0002] Although applicable to arbitrary micromechanical components andstructures, in particular sensors and actuators, the present invention,as well as the problem on which it is based, is explained in relation toa micromechanical acceleration sensor that can be manufactured insilicon surface micromechanical technology.

[0003] Acceleration sensors, and in particular micromechanicalacceleration sensors in surface micromechanical or volumemicromechanical technology, are gaining increased market share in thearea of motor vehicle equipment, and are increasingly replacing thepreviously standard piezoelectric acceleration sensors.

[0004] Standardly, the known micromechanical acceleration sensorsoperate in such a manner that, upon being deflected, the spring-mountedseismic mass device, which can be deflected in at least one direction byan external acceleration, effects a change of capacitance in adifferential capacitor device connected therewith, this change being ameasure of the acceleration.

[0005] The sensitivity of such known micromechanical accelerationsensors, e.g. for the measurement quantity acceleration, is currentlyset essentially by the rigidity of the spring mounting of the seismicmass, i.e., by the spring constant thereof. The associated specificintegrated electrical circuit (ASIC) permits adjustment only in arelatively small range of sensitivity.

[0006] Micromechanical acceleration sensors for maximum accelerationsbetween e.g. 2 g and 50 g (where g=acceleration due to gravity) arecurrently set only through differing spring rigidities; here, as a rule,there is little variation in the seismic masses.

[0007] Thus, in the known acceleration sensors it has turned out to bedisadvantageous that different layouts are required for differentmaximum accelerations, and adjustment is possible only within a verysmall range.

ADVANTAGES OF THE INVENTION

[0008] The micromechanical component according to the present invention,having the features of claim 1, has the advantage that the springrigidity can be adjusted in gradual fashion in a pre-measurement stageor a final measurement stage, so that a single layout or design can beused for a wide range of rigidities.

[0009] The idea on which the present invention is based is that in themicromechanical component, a structure that is or can be mechanicallyfixed, formed as a spring, can be unlocked or locked in order to set theeffective rigidity of the flexible spring device in step-by-stepfashion. For this purpose, two or more spring elements, having the sameor different rigidities, are situated in series and/or in parallel, anda desired effective spring constant is set.

[0010] In the subclaims, advantageous developments and improvements ofthe micromechanical component indicated in claim 1 are given.

[0011] According to a preferred development, the mass is connected witha first spring element that can be moved in relation to the substrate,and is connected with one end of a second spring element via a firstconnecting web. At the first connecting web, a first anchoring structurethat can be isolated is provided, for the isolatable anchoring of thefirst connecting web in relation to the substrate. In this way, anadjustable connection in series of at least two spring elements can berealized.

[0012] According to a further preferred development, the firstisolatable anchoring structure has at least one first isolation regionthat can be isolated through the application of electrical current. Thisis a useful method for disconnecting a mechanical connection by melting,in a manner comparable to an electrical fuse.

[0013] According to a further preferred development, the firstisolatable anchoring structure has two first isolation regions, whichare provided at two opposite sides of the first connecting web. In thisway, a stable, symmetrical anchoring can be realized.

[0014] According to a further preferred development, the second springelement is connected with one end of a third spring element via a secondconnecting web. At the second connecting web, a second isolatableanchoring structure is provided for the isolatable anchoring of thesecond anchoring web in relation to the substrate. In this way,additional spring elements can be connected in series in an analogousfashion.

[0015] According to a further preferred development, the secondisolatable anchoring structure has at least one second isolation regionthat can be isolated through the application of electrical current.

[0016] According to a further preferred development, the secondisolatable anchoring structure has two second isolation regions that areprovided at two opposite sides of the second connecting web.

[0017] According to a further preferred development, the respectivefirst and/or second isolation region has a first current line that isconnected with the relevant isolatable anchoring structure, and a secondcurrent line that is connected with the flexible spring device,preferably with an anchoring thereof. In this way, the isolating currentconnection can be realized without a large additional expense.

[0018] According to a further preferred development, the first andsecond isolation region, or the first and second isolation regions, havedifferent first current lines, so that they can be isolated selectively.

[0019] According to a further preferred development, the first andsecond isolation region, or the first and second isolation regions, havethe same first current line and have different cross-sections, so thatthey can be selectively isolated. This design saves the provision ofdifferent first current lines for the isolation.

[0020] According to a further preferred development, the mass isconnected with a first spring element that can be moved in relation tothe substrate, and is connected, via a first connecting web, with oneend of a second spring element. At the first connecting web, a firstcontrollable anchoring structure is provided for the controllableanchoring of the first connecting web in relation to the substrate. Acontrollable anchoring structure has the advantage that it can beswitched between the locked and unlocked states in reversible fashion.Moreover, in this way, in principle a continuous controlling (i.e.,without gradations) of the effective spring constant is possible.

[0021] According to a further preferred development, the firstcontrollable anchoring structure has at least one first isolation regionthat can be controlled by a generator device for a magnetic orelectrical field. In this way, a contactless controlling can beachieved.

[0022] According to a further preferred development, the firstcontrollable anchoring structure has two first isolation regions thatare provided at two opposite sides of the first connecting web.

[0023] According to a further preferred development, the second springelement is connected, via a second connecting web, with one end of athird spring element. At the second connecting web, a secondcontrollable anchoring structure is provided for the controllableanchoring of the second connecting web in relation to the substrate.

[0024] According to a further preferred development, the secondcontrollable anchoring structure has at least one second isolationregion that can be controlled by a generator device for a magnetic orelectrical field.

[0025] According to a further preferred development, the secondcontrollable anchoring structure has two second isolation regions thatare provided at two opposite sides of the second connecting web.

DRAWINGS

[0026] Exemplary embodiments of the invention are shown in the drawing,and are explained in more detail in the following description.

[0027] The Figures show:

[0028]FIG. 1 a top view of an acceleration sensor according to a firstspecific embodiment of the present invention; and

[0029]FIG. 2 a top view of an acceleration sensor according to a secondspecific embodiment of the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0030] In the figures, identical reference characters designateidentical or functionally identical components.

[0031]FIG. 1 shows a top view of an acceleration sensor according to afirst specific embodiment of the present invention.

[0032] In FIG. 1, 1 designates a micromechanical acceleration sensor, 3designates a seismic mass, 4 designates a substrate, 10 a-f designatemovable electrodes attached to seismic mass 3, 11 a-h designate fixedelectrodes anchored in stationary fashion in substrate 4, 60 or 600designate anchoring regions in substrate 4, C1 and C2 designatecapacitor terminal connections, CL1 and CL2 designate capacitor terminallines, F1, F2, F3 designate spring elements of the flexible springdevice, T1 and T2 designate isolation terminal connections, T1 a, T1 b,and T2 a, T2 b, designate isolation lines, V12 designates a connectingweb between F1 and F2, and V23 designates a connecting web between F2and F3. VF designates a connecting web between seismic mass 3 and firstflexible spring element F1, and VA designates a connecting web betweenthird flexible spring element F3 and anchoring 600.

[0033] Micromechanical acceleration sensor 1 according to this firstspecific embodiment is constructed in such a way that its seismic mass 3can be deflected as a result of accelerations in the x direction. Here,seismic mass 3 is suspended in elastic fashion over substrate 4 viaflexible spring device F1, F2, F3. Flexible spring device F1, F2, F3 isin turn anchored in the substrate via anchoring 600, but in the depictedstate is also connected via connecting webs V12 or V23 and correspondingisolation regions T1 a, T1 b, or T2 a, T2 b, which are each connectedwith an anchoring 60.

[0034] When there is a deflection in the x direction, a change ofcapacitance can be noted at terminal connections C1 and C2 of thedifferential capacitor device constructed from fixed electrodes 11 a-hand movable electrodes 10 a-f; this change of capacitance is a measureof the deflection.

[0035] In the exemplary embodiment shown in FIG. 1, three springelements F1, F2, F3 having different rigidities are therefore situatedone after the other, i.e., in a series circuit.

[0036] Here, for example, the more rigid spring element F1 is connecteddirectly to seismic mass 3; the softer springs F2, F3 are coupled onthrough the respective connecting web V12 or V23. In the state shown inFIG. 1, however, only first spring element F1 is effective for thespring loading, because, as stated, the other two spring elements F2 andF3 are anchored in the substrate via the respective connecting web V12or V23 and an anchoring structure 60; T1 a, T1 b or 60; T2 a, T2 bconnected thereto.

[0037] This mechanical anchoring can be realized both in the epitaxialpolysilicon for the electrodes and seismic mass 3 and also in the buriedpolysilicon for buried printed conductors. In this specific embodiment,it is realized in the epitaxial polysilicon. The details of this processare known in the prior art, and require no additional explanation here.

[0038] Via isolation terminal connections T1 and T2, an electricalcurrent can be applied through isolation line TL1, anchoring 60, therespective isolation region T1 a, T1 b or T2 a, T2 b, the relevantconnecting web V12, V23, and back to anchoring 600 and isolation lineTL2 via spring elements F2 or F3 and connecting web VA. The anchoring ofsecond spring element F2 or of third spring element F3 can beselectively isolated through this flow of current, thus setting a lowereffective spring constant for the flexible spring device as a whole.This process is comparable to the burning through of an electricalsingle-use fuse when overloaded.

[0039] A suitable choice of the geometry or of the layer construction ofthe isolation regions allows the determination of the precise locationfor the isolation, and, given a plurality of spring elements, alsoenables the selection of the isolation region that is to be isolated ata particular current value. In general, in this specific embodiment thedirected isolation of the structures in the isolation regions can takeplace through different electrical resistances in a common current line,and not only through different cross-sections or, for example, separateelectrical supply lines.

[0040] If the structures are realized in epitaxial silicon, an aluminumlayer can optionally be applied on partial areas of the structures forthe local adaptation of the resistance.

[0041] In the example shown in FIG. 1, isolation regions T1a and T1bhave a smaller cross-section than do isolation regions T2 a and T2 b. Itis therefore to be expected that when there is a flow of current throughthis parallel system, isolation regions T1 a and T1 b will melt first,at a first, lower current, and isolation regions T2 a and T2 b will notmelt until later, at a second, higher current, so that first the secondspring element F2, and then third spring element F3, can be activated instep-by-step fashion.

[0042] The isolation can take place both during electricalpre-measurement and also during electrical final measurement. Thedirected isolation can be monitored through the chronological curve ofthe current-voltage values in this process. The effective springconstant that is set for the flexible spring system can be determinedduring pre-measurement for example via the resonant frequency, and canbe determined during the final measurement for example via thesensitivity.

[0043]FIG. 2 shows a top view of an acceleration sensor according to asecond specific embodiment of the present invention.

[0044] In FIG. 2, in addition to the already-introduced referencecharacters, T1 a′, T1 b′, T2 a′, T2 b 40 designate a respectivecontrollable isolation region, T1′ and T2′ designate a respectivemodified isolation terminal connection, and TL1′ and TL2′ designatemodified isolation lines.

[0045] In this second specific embodiment, in the isolation region agenerator device for a magnetic field is provided; here the electricalfield strength can be controlled through the voltage applied at T1′ andT2′ (here, TL1′ and TL2′ are corresponding multiwire leads). In thisway, the effective spring constant of the overall flexible spring devicecan be set quasi-continuously as a function of the generated magneticfield.

[0046] In other respects, the second specific embodiment is identicalwith the first specific embodiment.

[0047] Although the present invention has been described above on thebasis of a preferred exemplary embodiment, it is not limited thereto,but rather can be modified in many ways.

[0048] In particular, the invention can be applied to arbitraryspring-mounted micromechanical components, and not only to accelerationsensors.

[0049] For example, arbitrary micromechanical base materials can beused, and not only the silicon substrate indicated as an example.

[0050] Although in the above example the isolation regions areelectrical melt-through regions, the isolation regions can also beinfluenced in other ways. Thus, the isolation can be carried out incontactless fashion, for example using a laser.

[0051] Likewise, the contactless controlling of the effective springconstant can be realized by an electrical field, rather than by amagnetic field.

[0052] The geometry of the spring system is also not limited to theindicated series circuit of three spring elements; rather, an arbitraryseries circuit/parallel circuit can have a multiplicity of springelements whose effective spring constant can be externally influenced.

What is claimed is:
 1. A micromechanical component, in particular anacceleration sensor, having a flexible spring device (F1, F2, F3) forthe spring mounting of a mass (3) over a substrate (4), the flexiblespring device (F1, F2, F3) being connected on the one hand with the mass(3) and on the other hand being anchored in the substrate (4); whereinthe flexible spring device (F1, F2, F3) has at least one flexible springelement (F2, F3) whose movability in relation to the substrate (4) iscapable of being modified in order to modify the effective springconstant of the flexible spring device (F1, F2, F3).
 2. Themicromechanical component as recited in claim 1, wherein the mass (3) isconnected with a first spring element (F1) that is capable of beingmoved in relation to the substrate (4), and is connected, via a firstconnecting web (V12), with one end of a second spring element (F2); andwherein a first isolatable anchoring structure (60; T1 a, T1 b) isprovided at the first connecting web (V12), for the isolatable anchoringof the first connecting web (V12) in relation to the substrate (4). 3.The micromechanical component as recited in claim 2, wherein the firstisolatable anchoring structure (60; T1 a, T1 b) has at least one firstisolation region (T1 a, T1 b) that is capable of being isolated throughthe application of electrical current.
 4. The micromechanical componentas recited in claim 3, wherein the first isolatable anchoring structure(60; T1 a, T1 b) has two first isolation regions (T1 a, T1 b) that areprovided at two opposite sides of the first connecting web (V12).
 5. Themicromechanical component according to one of the preceding claims 2 to4, wherein the second spring element (F2) is connected, via a secondconnecting web (V23), with one end of a third spring element (F3), andwherein, at the second connecting web (V23), a second isolatableanchoring structure (60; T2 a, T2 b) is provided for the isolatableanchoring of the second connecting web (V23) in relation to thesubstrate (4).
 6. The micromechanical component as recited in claim 5,wherein the second isolatable anchoring structure (60; T2 a, T2 b) hasat least one second isolation region (T2 a, T2 b) that is capable ofbeing isolated through the application of electrical current.
 7. Themicromechanical component as recited in claim 6, wherein the secondisolatable anchoring structure (60; T2 a, T2 b) has two second isolationregions (T2 a, T2 b) that are provided at two opposite sides of thesecond connecting web (V23).
 8. The micromechanical component as recitedin one of claims 3, 4, 6, 7, wherein the respective first and/or secondisolation region (T1 a, T1 b ; T2 a, T2 b) has a first current line(T1L) that is connected with the relevant isolatable anchoring structure(60; T1 a, T1 b; T2 a, T2 b), and a second current line (TL2) that isconnected with the flexible spring device (F1, F2, F3), preferably withan anchoring (600) thereof.
 9. The micromechanical component as recitedin one of claims 3, 4, 6, 7, 8, wherein the first and second isolationregion (T1 a, T1 b; T2 a, T2 b), or the first and second isolationregions (T1 a, T1 b; T2 a, T2 b), have different first current lines, sothat they are capable of being selectively isolated.
 10. Themicromechanical component as recited in one of claims 3, 4, 6, 7, 8,wherein the first and second isolation region (T1 a, T1 b; T2 a, T2 b),or the first and second isolation regions (T1 a, T1 b; T2 a, T2 b), havethe same first current line (TL1) and have different cross-sections, sothat they are capable of being selectively isolated.
 11. Themicromechanical component as recited in claim 1, wherein the mass (3) isconnected with a first spring element (F1) that is capable of beingmoved in relation to the substrate (4), and is connected, via a firstconnecting web (V12), with one end of a second spring element (F2), andwherein a first controllable anchoring structure (60; T1 a′, T1 b′) isprovided at the first connecting web (V12), for the controllableanchoring of the first connecting web (V12) in relation to the substrate(4).
 12. The micromechanical component as recited in claim 11, whereinthe first controllable anchoring structure (60; T1 a′, T1 b′) has atleast one first isolation region (T1 a′, T1 b′) that is capable of beingcontrolled by a generator device for a magnetic or electrical field. 13.The micromechanical component as recited in claim 12, wherein the firstcontrollable anchoring structure (60; T1 a′, T1 b′) has two firstisolation regions (T1 a′, T1 b′) that are provided at two opposite sidesof the first connecting web (V12).
 13. The micromechanical component asrecited in one of the preceding claims 11 to 13, wherein the secondspring element (F2) is connected, via a second connecting web (V23),with one end of a third spring element (F3), and wherein a secondcontrollable anchoring structure (60; T2 a′, T2 b′) is provided at thesecond connecting web (V23) for the controllable anchoring of the secondconnecting web (V23) in relation to the substrate (4).
 14. Themicromechanical component as recited in claim 13, wherein the secondcontrollable anchoring structure (60; T2 a′, T2 b′) has at least onesecond isolation region (T2 a, T2 b) that is capable of being controlledthrough a generator device for a magnetic or electrical field.
 15. Themicromechanical component as recited in claim 14, wherein the secondcontrollable anchoring structure (60; T2 a′, T2 b′) has two secondisolation regions (T2 a, T2 b) that are provided at two opposite sidesof the second connecting web (V23).